I see that most of this was put in there as a kind of a note-to-self originally, however _SC_NPROCESSORS_ONLN is implemented by every realistically possible targets anyway, so for all practical purposes, this is dead weight.

A couple of questions remain, though:

#ifdef Q_OS_WIN32 should probably be Q_OS_WIN, so as to include win64 as well.

Assuming the real purpose for this function is to determine how many parts a particular task is to be split into in the future, if and when QCAD gets the need to split expensive tasks among multiple CPUS, “core” probably shouldn’t be static - CPUs are hot-pluggable today, and while one probably doesn’t do that on a laptop, it’s not unfeasible in, say, a VDI environment.